ABBREVIATIONS3GPP3rd Generation Partnership ProjectACKAcknowledgementBPSKBinary Phase-shift KeyingCAMCooperative Awareness MessageCDMCode Division MultiplexingCPCyclic PrefixD2D or ProSeDevice to Device communication, direct communicationDFTDiscrete Fourier TransformDLDownlinkDSRCDedicated Short Range CommunicationETSIEuropean Telecommunications Standards InstituteFDMFrequency Division MultiplexingFDMAFrequency Division Multiple accessIEEEInstitute of Electrical and Electronics EngineersINDIndicatorLTELong Term EvolutionLTE-ALTE-AdvancedLTE-D2DLTE based Direct communicationLTE-PC5LTE based Sidelink air interfaceMAC-PDUMedium Access Control - Packet Data UnitNACKNegative AcknowledgmentOFDMAOrthogonal Frequency Division Multiple AccessPRBPhysical Resource BlockProSeProximity ServicesPSCCHPhysical Sidelink Control ChannelPSSCHPhysical Sidelink Shared ChannelQPSKQuadrature Phase Shift KeyingRBResource BlockREResource ElementRXReceiveSAScheduling AssignmentSC-FDMASingle Carrier - FDMASCISidelink Control informationSCI-ACK-INDSCI acknowledgement indicatorSC-PeriodSidelink Communication PeriodSidelinkUE to UE interface for sidelink communicationand sidelink discoveryTRP or T-RPTTime Resource PatternTXTransmitULUplinkV2IVehicle to Infrastructure communicationV2PVehicle to Pedestrian communicationV2VVehicle to Vehicle communication or communicationbetween vehiclesV2XVehicle to Everything communicationVANETVehicular Ad-Hoc NetworkVC-PeriodSidelink communication period for V2X communicationor V2X Communication PeriodWAVEWireless Access for Vehicular Environment
Vehicle-to-Everything (V2X) communication enables vehicles to communicate with other vehicles (i.e. Vehicle-to-Vehicle (V2V) communication), with infrastructure such as traffic lights (i.e. Vehicle-to-Infrastructure (V2I) communication), with pedestrians (i.e. Vehicle-to-Pedestrian (V2P) communication, and even with the owner's home (i.e. Vehicle-to-Home (V2H) communication).
V2X systems can be used in a wide range of scenarios, including in relation to road safety, where it has been estimated that V2X systems can prevent over 80 percent of accidents by unimpaired drivers by alerting the drivers to hidden dangers that can't be sensed by traditional on-board equipment such as sensors.
In related to traffic efficiency, V2X systems, in combination with a nationwide data collection and processing network, may further facilitate environmental improvements, as well as improvements to public safety, mobility, productivity and convenience, by providing optimised traffic routing, traffic flow, traffic control and incident management.
In V2V communication, data may be shared between V2X-equipped vehicles within a half-mile or 800 m radius of each other, which can be used to provide a driver with a global view of traffic and be alerted to the most common causes of accidents in time to take evasive action. In more advanced applications, an evasive action may be initiated by the receiving vehicle automatically.
Various radio access technologies, including IEEE 802.11a in DSRC and IEEE 802.11p in WAVE or VANET, have been considered for V2X systems. However, IEEE 802.11 based radio access technologies are unnecessarily complex, and more suitable for non-deterministic message transmission. In particular, V2X services generally require deterministic and low latency message transmission, whereas 802.11 based technology is generally high latency.
Recently, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) technology has been considered for V2X services. 3GPP LTE technology is being deployed all over the world and at a rapid pace, which enables more and more advanced services and internet applications that utilise the higher data rate, lower latency, and enhanced coverage that 3GPP LTE provides. Widely deployed LTE-based networks provide opportunities for the vehicle industry to realise the concept of “connected cars”.
Furthermore, recently standardised 3GPP Release 12 device-to-device (D2D) or ProSe feature enables devices to directly communication over a side-link (PC5) radio interface without network coverage. As such, these standards have attracted strong interest from vehicle manufacturers and other road-safety agencies as a candidate for vehicular communication.
Technically, LTE-D2D or LTE-PC5 technology, and especially sidelink (PC5) interfaces, are suitable for use in V2X communication, and in particular in V2V/V2I communication in and/or out of network coverage, where distributed resource allocation is essential.
However, data collision, especially where there are high numbers of V2X terminals within close proximity to one another, or outside the transmission range of each other, is a problem when LTE technology is used for V2X communication.
In particular, in a communication period (SC-Period), there is a high probability that more than one V2X terminal will select the same channel index for control channel transmission, causing a collision. Furthermore, legacy V2X communication employs half-duplex technology, which prevents a V2X terminal from detecting the collision, because on subframes allocated for transmission a V2X terminal cannot simultaneously listen for data from other V2X terminals. Furthermore, collision on a control channel directly results in message loss and may lead to further collisions on data channels.
FIG. 1A illustrates a part of an exemplary scenario 100, according to the related art, where collision on unicast is illustrated. FIG. 1B illustrates the remaining part of the exemplary scenario 100, according to the related art, where collision on unicast is illustrated.
First and second V2X terminals 101, 102 are within close proximity of each other and have the same transmission range 103. On an SC-Period 110, both the first and second V2X terminals 101, 102 happen to have data to transmit to a third V2X terminal 105. In a PSCCH subframe pool 111 within the SC-Period 110, both the first and second V2X terminals 101, 102 happen to select the same control channel index 112 (i.e. channel index “0”) for transmitting SCI. This results in full collision at the third V2X terminal 105, and as such, the third V2X terminal cannot detect and decode the SCI transmitted by either the first or second V2X terminal 101, 102.
As the first and second V2X terminals 101, 102 are unaware of the collision, both V2X terminals 101, 102 transmit MAC-PDUs on PSSCHs in an associated PSSCH pool 115. These transmitted MAC-PDUs will be unheard by the third V2X terminal 105 as no control information has been detected.
In case one-to-one mapping is provided between the control channel index and a T-RPT pattern, further collision 117 occurs in relation to the PSSCH. As the SCI was not detected and decodable at the third V2X terminal 115, the transmission of the SCI on the PSSCHs merely caused noise and interference to other near V2X terminals.
Technically, random back-off may be employed at the first and second V2X terminals 101, 102 where each V2X terminal 101, 102 randomly selects a delay before transmitting the SCI. However, this introduces additional delay. Furthermore, the network topology may change when V2X terminals 101, 102 move rapidly, and such latency may actually lead to collisions with other, incoming V2X terminals.
FIG. 2 illustrates an exemplary scenario 150, according to the related art, where collision on broadcast/groupcast is illustrated.
First and second V2X terminals 151, 152 belong to the same group, are in close proximity of each other and have the same transmission range 150.b. As such, the first and second V2X terminals 151, 152 are aware of the presence to each other.
On an SC-Period, both V2X terminals 151, 152 happen to have data to transmit to other V2X terminals 155, 156, 157, 158 in the same group, and happen to select the same control channel index 153 (i.e. channel index “0”) for transmitting SCI.
This results in full collision at the other V2X terminals 155, 156, 157, 158. As such, the other V2X terminals 155, 156, 157, 158 cannot detect and decode the SCI. The V2X terminals 151, 152 are unable to detect if a collision has happened, and as such, both V2X terminals 151, 152 transmit MAC-PDUs on PSSCHs in the associated PSSCH pool, which causes further collision.
When hidden terminals are present, the collision can be more severe as two or more V2X transmitters may not be aware of the presence of each other because they are out-of-transmission range with each other. FIG. 3 illustrates an exemplary scenario 170, according to the related art, where collision caused by a hidden terminal is illustrated.
A first V2X terminal 171 having a first transmission range 172, and a second V2X terminal 173 having a second transmission range 174, are out-of-transmission range of each other, and as such, are not aware of the presence of each other. On an SC-Period, both V2X terminals 171, 173 happen to have data to transmit to a third V2X terminal 175, which in turn has a third transmission range 176 covering both V2X terminals 171, 173.
Both V2X terminals 171, 173 happen to select the same control channel index “0” in a PSCCH subframe pool, for transmitting SCI 180. This results in full collision 181 at the third V2X terminal 175, and as such, the V2X terminal 175 cannot detect and decode the SCI. Since the V2X terminals 171, 173 are unable to detect the collision 181, both V2X terminals 171, 173 transmit MAC PDUs on PSSCHs 190, 191 in the associated PSSCH pool.
In the case there is one-to-one mapping between control channel index and TRP, further collision 192 on PSSCHs transmission occurs at the V2X terminal 175.
As the SCIs were not detected and decodable at the V2X terminal 175, the transmission of the data merely increases noise and interference for other V2X terminals.
In certain circumstances, for example due to differences in channel gain between the first V2X terminal 171 and the third V2X terminal 175, and between the second V2X terminal 173 and the third V2X terminal 175, the third V2X terminal 175 may detect and decode SCI transmitted from one of the V2X terminals 171, 173 but not the other. However, further PSSCH transmission 190, 191 from the V2X terminals 171, 173 results in data collision.
Accordingly, there is a need for improved Vehicle to Everything (V2X) data communication.
It will be clearly understood that, if a related art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.